The Role of Mycotoxins in Interactions between Fusarium graminearum and F. verticillioides Growing in Saprophytic Cultures and Co-Infecting Maize Plants.

() and () co-occur in infected plants and plant residues. In maize ears, the growth of is stimulated while is suppressed. To elucidate the role of mycotoxins in these effects, we used mutants with disrupted synthesis of nivalenol (NIV) and deoxynivalenol (DON) and a mutant with disrupted synthesis of fumonisins to monitor fungal growth in mixed cultures in vitro and in co-infected plants by real-time PCR. In autoclaved grains as well as in maize ears, the growth of was stimulated by regardless of the production of DON or NIV by the latter, whereas the growth of was suppressed. In autoclaved grains, fumonisin-producing suppressed FG more strongly than a fumonisin-nonproducing strain, indicating that fumonisins act as interference competition agents. In co-infected maize ears, suppression was independent of fumonisin production by , likely due to heterogeneous infection and a lower level of fumonisins in planta. We conclude that (i) fumonisins are agents of interference competition of , and (ii) trichothecenes play no role in the interaction between and . We hypothesize the following: (i) In vitro, stimulates the growth by secreting hydrolases that mobilize nutrients. In planta, suppression of plant defense by may additionally play a role. (ii) The biological function of fumonisin production in planta is to protect kernels shed on the ground by accumulating protective metabolites before competitors become established. Therefore, to decipher the biological function of mycotoxins, the entire life history of mycotoxin producers must be considered.